In systems for handling mixed mail or other flat articles, which may or may not be of a uniform size, the articles are frequently stacked on edge and passed through a singulation mechanism at the beginning of the operation. However, particularly where there are significant variations in the size, thickness and weight for the articles being singulated, the singulator will it from time to time pass two or more pieces of mail or other articles simultaneously, a smaller article for example piggy-backing on a larger article being singulated. This problem, which is commonly referred to as doubles or multiple feeds, if left unresolved, can possibly lead to missorts, damage to the articles, rejects or jams in downstream parts of the system. While many techniques have been employed in the past to resolve such doubles, particularly in mail handling systems, the variations in size, weight and thickness of mixed mail make doubles very difficult to resolve. For example, one specification for a mixed mail handling system requires handling mail vary in size from 4".times.4" or 3.5".times.5.0" to 15".times.15", weights from a 0.03 ounces to six pounds and thickness from 0.007" up to 1.25 inches. Further, some of the larger pieces may be soft covered magazines, catalogs, telephone books or the like which are bound on only one edge, further complicating the singulation and doubles resolving process. Mechanisms for successfully resolving doubles at the output of a singulator in a system handling articles of mixed size, thickness and weight with variations on the order of those indicated above do not currently exist.